This invention relates generally to transformers and more particularly, but not by way of limitation, to a transformer which provides two three-phase outputs out of phase with each other. The present invention also relates to a pumping system using the transformer to energize a pump motor either through a twelve-pulse rectifier requiring the two out of phase three-phase outputs or through a by-pass motor controller actuating the motor directly with a single one of the three-phase outputs.
Multiple phase transformers, such as ones providing three-phase outputs as will be referred to herein for convenience, are typically used in systems having similar loads which can all be energized using a single three-phase output from the transformer. Some systems, however, require different types of outputs which heretofore might have required different transformers.
By way of an example, reference will be made to an oil pumping system having an electric submersible pump powered by a three-phase induction motor controlled through a speed control variable frequency drive (electronic frequency converter). This type of variable speed drive typically includes a twelve-pulse rectifier which requires two three-phase inputs which are 30.degree. out of phase. This type of rectifier is maintenance intensive so that during maintenance of the rectifier, the electric motor driving the submersible pump must be powered by the same transformer but with the rectifier by-passed. This by-pass requires only a single three-phase output, but one capable of handling the entire load presented by the electric motor which drives the pump.
From the foregoing example, there is the need for a type of transformer which can supply power to a twelve-pulse rectifier such as those used in electronic frequency converters. Such transformer must alternately supply power directly to a three-phase load such as an induction motor. More specifically, there is the need for a single transformer having six outputs that can be switched to drive a three-phase load either through a device which needs two out of phase three-phase outputs or directly. It would be desirable if such a transformer could be implemented through one or more designs having a smaller equivalent transformer size relative to an isolation transformer. There is also the specific need for a pumping system utilizing such a transformer.